Climatic influences on active layer depth between 2000 and 2018 in the McMurdo Dry Valleys, Ross Sea Region, Antarctica

The maximum seasonal depth of thaw (the active layer depth) in permafrost soils is influenced by a range of soil and atmospheric variables. The active layer depth and the temperature at the top of the permafrost have potential to provide a clear signal of a changing climate, damping out noise more effectively than atmospheric variables. A monitoring network of nine soil climate stations was established in the McMurdo Dry Valleys between 1999 and 2012. Each station monitors soil temperature to a depth of up to 1.2 m, along with a range of atmospheric variables including air temperature, solar radiation, and wind speed. Over the period of record included in this study (2000-2018): the mean active layer depth ranged from 7.6 cm at Mt. Fleming to >90 cm at Granite Harbour; the mean annual shallow (15 cm) soil temperature ranged from -24 degrees C at Mt. Fleming to -14 degrees C at Granite Harbour; and the mean summer air temperature ranged from -11 degrees C at Mt. Fleming to -1 degrees C at Granite Harbour. There was marked between-year variation but no significant trends of increase or decrease in active layer depth, or temperature at the top of the permafrost, between 2000 and 2018. Wavelet analysis showed that both global and regional climate systems correlated with de-seasonalised temperature at the top of the permafrost. The Southern Annular Mode had relationships at both annual and biannual timescales (p < 0.05); the Southern Oscillation Index had a relationship at a 2-3 year timescale (p < 0.05); and the Amundsen Sea Low had an annual signal and some between season signals (p < 0.05). The data set is too short to draw conclusions on potential longer-term changes in the soil climate. Nevertheless, the database provides a baseline against which future change can be assessed and will increase in value the longer it is maintained.

Automated summary

The maximum seasonal depth of thaw in permafrost soils, known as the active layer depth, is influenced by various soil and atmospheric variables. Monitoring data from soil climate stations in the McMurdo Dry Valleys between 1999 and 2012 revealed significant variations in active layer depth and temperature at the top of the permafrost. However, there were no clear trends of increase or decrease during the period from 2000 to 2018. Wavelet analysis showed correlations between global and regional climate systems and de-seasonalized permafrost temperatures. Although the dataset is currently too short to draw conclusions about long-term changes, it serves as a valuable baseline for future assessments.